The Science Behind How Furry Animals Shake To Get Dry

David Hu sprays animals with water and and videotapes the results.

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The Science Behind How Furry Animals Shake To Get Dry
Yogi the dog shakes off some excess water following a dip. Photo:Flickr Creative Commons, Soggydan
The Science Behind How Furry Animals Shake To Get Dry
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The Science Behind How Furry Animals Shake To Get Dry

Using high-speed video cameras, hoses, and a healthy dose of bravery, David Hu’s lab is studying the science behind how wet animals get dry.

The team sampled everything from mice to dogs and even took a trip to a zoo in Atlanta, where they sprayed down a bear and watched how it dried off. 
“My grad student had the pleasure of going into the animal cages with a hose and a high speed camera," joked Mr. Hu, an assistant professor of mechanical engineering at Georgia Institute of Technology.
Getting dry quickly is critical in the wild, Mr. Hu said. If a wet animal can't dry itself, it could face hypothermia.
After studying the tapes of 33 different animals, Mr. Hu's lab found the most effective shakers were mice, which dried off by shaking at a rate of 30 times per second. That's enough energy to throw water with a force equivalent to about 70 times standard Earth gravity.
Humans, by contrast, can only move their heads back and forth about twice per second.
“Imagine coming out of your shower and pressing this button and getting 70 percent dry in a tenth of a second.” Mr. Hu explained. “[Mice] get instantaneously get dry."
Dogs, on average, took about three-quarters of a second to dry off. Mr. Hu said most animals gave about three shakes to get rid of excess water and that all animals closed their eyes while shaking, potentially to prevent damage to their retinas due to the high forces involved.
Mr. Hu's team also noted the loose skin on furry animals helps increase the amplitude - and thereby efficiency - of a good shake. 
"For many years evolutionary biologists had noticed that all furry animals have loose skin, but no one had known why," Mr. Hu said.
The practical applications for studying shaking animals could be wide-ranging. Mr. Hu's lab is working to implement their findings into robotics, where autonomous cleaning devices could potentially shake and clear the dust off the solar panels attached to a stalled rover on the surface of Mars or another planet.
Mr. Hu said he comes from a mechanical engineering background, but he’s always been fascinated by biology. Today, his lab focuses on natural ways animal repel water. And while a graduate student at MIT, he worked to build a robot mimicking the way a water strider moves across the surface of a lake
“I think that was sort of a formative experience for me.” Mr. Hu said. “Seeing that there’s so much low-lying fruit in nature. If we want to build better devices that can tackle all this different terrain, nature’s already done it. We just need to figure out how she did it.”
**Video courtesy Nature Magazine**